Various electro-optical systems have been developed for reading optical indicia, such as bar codes. A bar code is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths, the bars and spaces having differing light reflecting characteristics. Systems that read and decode bar codes employing CCD or CMOS-based imaging systems are typically referred to as imaging-based bar code readers or bar code scanners.
The bar code reader includes an imaging and decoding system including an imaging system for generating an image of a target bar code and decoding circuitry for decoding the imaged target bar code. Imaging systems include CCD arrays, CMOS arrays, or other imaging pixel arrays having a plurality of photosensitive elements or pixels. Light reflected from a target image, e.g., a target bar code is focused through a lens of the imaging system onto the pixel array. Output signals from the pixels of the pixel array are digitized by an analog-to-digital converter. Decoding circuitry of the imaging and decoding system processes the digitized signals and attempts to decode the imaged bar code.
Two types of imaging system pixel arrays are typically used: a one dimensional (1D) imaging array and a two dimensional (2D) imaging array. A 1D imaging array is characterized by a single row of pixels, an 1×n array of 1 row and n columns of pixels, while a 2D imaging arrays is characterized by multiple rows and multiple columns, an m×n array of m rows and n columns of pixels.
In response to a need to include greater amounts of information in a bar code of limited overall horizontal width, high density bar codes have been developed which utilize bar code elements having very narrow widths. The ability of a 1D array imaging system to successfully decode a high density bar code is dependent upon blur and pixels per module (PPM). PPM refers to the number of pixels imaging the smallest, that is, narrowest element of the bar code. For example, a PPM of 1 would indicate that the narrowest element of the bar code is being imaged by a single pixel of the imaging array, a PPM of 2 would indicate that the narrowest element of the bar code is being imaged by two pixels of the imaging array. Advanced imaging systems are able to successfully read, that is, image and decode a bar code with a PPM low as 0.7. However, it is obvious that the ability of an imaging system to successfully read a high density bar code increases as PPM increases. The same is true for 2D array imaging systems.
One solution to reading high density bar codes is to use an imaging system with more pixels. However, increasing pixel count increases imaging system cost. What is needed is an imaging and decoding system for a bar code reader imaging system that provides for enhanced ability to read high density bar codes without the necessity of increasing the number of pixels.